Production of phosphorus and phosphoric acid



Patented Nov. 22, 1932 TENT OFFICE WILLIAM I-I. WAGGAIVZAN, OF LAKELAND,AND STAPLETON D. GOOCH, F LAKE WALES,

FLORIDA, ASSIGNORS T0 CORONET PHOSPI-IATE COMPANY, 0F NEW "YORK, N. Y.,AU:

CORPORATION or NEW Yon-K PRODUCTION OE' PIjISPHORUS AND PHOSPI-IORICACID AApplication led March 21, 1930. Serial No. 437,748.

This invention relates to the production-of phosphorus and phosphoricacid and more particularly to an improved method of and yapparatus forthe pyrolytic reduction of phosphatic material.

A well-known and widely used method of preparing phosphorus andphosphoric acid from phosphatic material comprises charging a mixture ofthis material with a siliceous flux and a suitable fuel to a fuelfurnace of the blast furnace type. At the high temperatures of operationthe silica displaces the phosphoric acid of the rook to form phosphoruspentoxide or, if reducing conditions are maintained, elementalphosphorus.

While blast furnaces have heretofore been employed for thisvolatilization process, little attention appears to have been paid tothe general problem of modification of the construction and design so asto secure more ef- -cient results. Blast furnaces of standard vsize andconstruction have been employed which conform generally to that typeused in the manufacture of pig iron and ferro alloys. y Little has beendone to modify such constructions in light vof the problemspeculiar tothe production of .phosphorus by this method. Tn the usual type ofapparatus the ratio of the height (from the hearth vto Vthe stock line)to the diameter of the furnace crucible has notv been over seven to one;as a matter of fact, this ratio rarely exceeds six to one.' Thislimitation in the height of the furnace seems to be due to the prevalentbelief that an increase in this ratio is impractical because of thedisadvantages resulting from the increased weight of stock and increasein resistance to the passage of gases. We have found that by speciallydesigning a blast 40 furnace and thereby departing from the conventionalstructures, and furthermore by sub jecting the material to be treated inthe furnace'to a special preliminary treatment, new and improved resultscan be secured.

It is a major object of the present invenvproducing phosphorus, of arelatively high tion, therefore, to provide an improved blast furnace sodesigned as to effectively and economically produce phosphorus and/orphosphoric acid.

Another object is to provide an improvedl process for producingphosphorus by the pyrolytic method by which high fuel economies areachieved.

A further object is Vto provide a process for degree of purity, by thepyrolytic method.

With these and other equally important objects in view, the inventioncomprehends the special preliminary treatment of a charge of phosphaticmaterial and the smelting of this' 60 charge in a blast furnace soconstructed and designed as to present a relatively high column ofstock.

In order to more clearly explain the invention, there is shown in theaccompanying drawing, an illustrative embodiment of the apparatusemployed.

This may comprise ablast furnace of any desired construction but havinga certain predetermined ratio of height to width and/or area of stockspace, as explained more fully hereinafter.

As shown in the drawing, such a furnace may in its general features ofconstruction. conform to theusual type having a tapered shaft and bellyof large diameter. More specilically, it may comprise, as shown, amantle or outer stack casing which is of any desired material, providedwith a shirt or lining 2 of some refractory such as fire brick. Ifdesired,/a stufng of sand or other suitable material or a second lining,may be interposed between the mantle and shirt.

The casing structure may be sustained by any suitable type of supportingmeans, as indicated convention ally on the drawing by the supportingelements 3. The complete casing encloses the shaft or fire room 4, whichmay taper, upon any predetermined inclination from the mouth to thebelly. Below the belly, 90

the shaft may be constricted in accordance with any approved design topresent the boshes 5, the subjacent hearth and Crucible sections 6 and 7respectively. .Ihe Crucible may be apertured adjacent the base or sole 8to provide a tap hole 9, through which the fused slag may be withdrawn.

Connected with any suitable source of hot air, is a conduit 10, whichfeeds the tuyeres 11. These, in the well-known manner, feed highlypreheated air to the mass to be smelted so as to effect the combustionof the carbonaceous fuel.

Positioned in the upper section of the furnace is a means for feedingthe charge thereto. For the purpose of simplifying the drawing, this isshown as a conventional bell and hopper 12, the end of which terminatesover a feed hole 13, which latter communicates, as shown, with theshaft. It will be understood that the element 12 is given as indicativeof any suitable type of feeding mechanism. It will also be appreciatedthat the feeding shaft 13 may be provided with any suitable type ofcheck mechanism, so as to prevent escape of gases through the feedingconduit. Also positioned in the upper section of the furnace is the gasdraw-off or downcomer 14, through which the gaseous products ofcombustion are withdrawn. These gases may be subjected to any desiredtype of subsequent treatment such, for example, as is described inco-pending application, Serial No. 434,142 filed Mar. 7 1930.

We have found, as indicated hereinbefore, that improved results may besecured if the ratio of the height of the stack, as measured from thehearth to the furnace stock line to the diameter of the furnaceCrucible, is increased so as to present a relatively high column ofstock. This is particularly true if the phosphatic material is subjectedto a preliminary treatment. In the preferred operation the phosphaticraw material is first sintered so as to provide a relatively lightinterstitial mass of phosphate and siliceous material.

I/Ve have found further that if the above mentioned ratio, i. e., theheight from the hearth 6 to the furnace stock line 15, bear arelationship of between seven and eight and one-half to one the width ofthe Crucible 7, improved results are secured.

This additional height of stock column is i very desirable. In the firstplace by providing a higher stack, the time element for the absorptionof heat by the phosphatic material by the furnace gases is increased,and the furnace gases are withdrawn and the phosphatic Charge enters thereaction zone of the furnace at a temperature at which phosphorus isalmost immediately evolved. In addition, the porous and permeable natureof an expanded or sintered charge presents much less resistance to thepassage of gases than does a heavier and more compact charge, andparticularly where the latter is quite dense, as in the case ofbriquettes and lumps of natural phosphate rock. When using a porouscharge of relatively greater height, the increase in gas velocity due tothe porosity of the charge is offset by providing a higher column ofstock, a longer path for the furnace gases, and an increase in theheatexchange area.

Furthermore, on account of the high temperatures employed in smeltingphosphate rock and siliceous material, a considerable amount of fumesand volatile products are evolved. By providing a longer column of stockthrough which the furnace gases can percolate or filter, agreater amountof these evolved materials are filtered out; that is to say, the longerstock column acts as a condensing or filtering medium to retain finelydivided products and impurities which, if passing o with the phosphorus,would adversely affect the value of .the product.

It will be appreciated, furthermore, that by mixing carbonaceous fuelwith the light sintered charge, a wider dispersion of a given quantityof fuel per volume of phosphatic material is secured. As the result ofthis, the combustion of the fuel is accelerated and rendered morecomplete. optimum utilization is made of fuel values and the heatgenerated by the combustion of the fuel is more evenly and uniformlydisseminated through the mass to be smelted.

In the preferred construction, therefore, we employ a. furnace of ablast furnace type of such dimension that the ratio of its height (fromthe base of the Crucible to the stock line) to the inside diameter ofthe Crucible is at least seven and one-half to one. A typical example ofsuch a structure is shown in the drawing in which a furnace having adistance of ninety feet from lthe Crucible to the stock line, has aCrucible or hearth diameter of twelve feet instead of seventeen feet, asis the usual width in a furnace of such a height.

In carrying out the process, a. sintered mass of phosphate and siliceousmaterial, is mixed with a predetermined quantity of coke or othercarbonaceous material and is fed to the blast furnace through the belland hopper 12, or equivalent feeding means. If desired, of course, thesintered phosphatic material and the fuel may be fed into the top of thefurnace through separate elements and at respectively correlated andpredetermined rates. During operation, a blast of air preheated to atleast 1400o F. is fed through the tuyres in the well-known manner. rIlhegaseous mixture and phosphorus vapor evolved by this treatment passesupwardly through the long column of stock and is discharged throughdowncomer 14, and thence through a dust catcher of conventional design.'Ihe phosphorus and any solid parti- In other words# cles stillcontained in the gases are then condensed out and treated to preparephosphoric acid as, for example, in the manner described in thecopending application above referred to.

' It will now be appreciated that we have provided an improved processand apparatus for preparing phosphorus by the pyrolytic method. Byaccurately correlating the physical character of the charge with respectto the area within the Zone of action, improved results are secured. Theexpanded or interstitial nature of the charge is fully utilized tosubserve the function of largely separating out or filtering solidlparticles, thereby diminishing the load on the purifying apparatus. Theheight of the charge is so regulated that optimum absorption of thesensible heat of the furnace gases is secured. This factor is ofpeculiar importance in the production of phosphorus because of the hightemperature of operation.

The thermal units required to smelt, a charge of phosphatic material andto reduce and volatilize the phosphorus are much greater than thoserequired in other blast furnace operations such, for example, as theproduction of pig iron and ferro alloys. It will be appreciated, in thepresent process, that these thermal economies are attributable in partto the physical character of the stock and in part to its dimensionalcharacteristics: thus the permeable nature of the charge permits arelatively free passage of the gases and thus insures more uniformheating in the upper portions of the column; the porosity of the chargeassures a high rate of area to volume and hence increases the heatcontacting or transfer surface; the elongated or extenuated character ofthe stock) with respect to the direction of flow of the gases) providean increased or protracted time of contact between the hot gases and thecharge, and thereby appreciably increases the total heat absorption.

In short, these improved advantages are achieved by the correlation ofthe physical character of the charge and the dimensional characteristicsof the charge as determined and fixed by the improved design of thefurnace.

It is to be understood, therefore, that while the typical apparatus hasbeen shown in the drawing and described in the specification, it is tobe understood that this is given merely for purposes of illustration andis to be considered as typical of any similar furnace structure which,in conjunction with the described physical character of the charge, willinsure the described beneficial results.

We claim:

A method of pyrolytically producing phosphorus from phosphatic materialcomprising charging a mixture consisting of a sintered mass of phosphateand siliceous material together with a fuel into a furnace zone,building the charge in the furnace zone until the height of the chargebears a ratio to the width of the charge of more than seven and onehalfto one, igniting the charge and passing the generated gases and vaporsupwardly through the elongated column-like charge, the height of whichis more than seven and one-half times the width, thereby effecting ahigh flow velocity of the gases and vapors and insuring a prolonged heatexchange pe. riod between the hot evolved gases and vapors and the uppersection of the charge.

In testimony whereof we affix our signatures.

WILLIAM H. WAGGAMAN. STAPLETON D. GOOCH.

